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Function Optimization

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Function Optimization

default function parameters

In C++, the parameters in a function's parameter list can have default values.

Grammar: 返回值类型 函数名 （参数= 默认值）{}

Example:

int func(int a, int b = 10, int c = 10) {
    return a + b + c;
}

//1. 如果某个位置参数有默认值，那么从这个位置往后，从左向右，必须都要有默认值
//2. 如果函数声明有默认值，函数实现的时候就不能有默认参数
int func2(int a = 10, int b = 10);
int func2(int a, int b) {
    return a + b;
}

int main() {

    cout << "ret = " << func(20, 20) << endl;
    cout << "ret = " << func(100) << endl;


    return 0;
}

运行结果：

ret = 50
ret = 120

Function Placeholder Parameters

In C++, function parameter lists can have placeholder parameters used as placeholders, and when calling the function, that position must be filled.

Syntax: 返回值类型 函数名 (数据类型){}

At this stage, the placeholder parameters in functions have little significance, but this technique will be used in later lessons.

Example:

//函数占位参数 ，占位参数也可以有默认参数
void func(int a, int) {
    cout << "this is func" << endl;
}

int main() {

    func(10,10); //占位参数必须填补


    return 0;
}

运行结果：

this is func

function overloading

Function Overloading Overview

Purpose: Functions can share the same name, improving reusability

Function overloading satisfies the conditions:

  • Under the same scope
  • Function names are the same
  • Different types of function parameters, or different counts, or different orders

Note: Return values cannot be used as conditions for function overloading.

Example:

//函数重载需要函数都在同一个作用域下
void func()
{
    cout << "func 的调用！" << endl;
}
void func(int a)
{
    cout << "func (int a) 的调用！" << endl;
}
void func(double a)
{
    cout << "func (double a)的调用！" << endl;
}
void func(int a ,double b)
{
    cout << "func (int a ,double b) 的调用！" << endl;
}
void func(double a ,int b)
{
    cout << "func (double a ,int b)的调用！" << endl;
}

//函数返回值不可以作为函数重载条件
//int func(double a, int b)
//{
//  cout << "func (double a ,int b)的调用！" << endl;
//}

int main() {

    func();
    func(10);
    func(3.14);
    func(10,3.14);
    func(3.14 , 10);
    

    return 0;
}

运行结果：

func 的调用！
func (int a) 的调用！
func (double a)的调用！
func (int a ,double b) 的调用！
func (double a ,int b)的调用！

Function Overloading Considerations

  • References as Overload Conditions
  • Function Overloading with Function Default Parameters

Example:

//函数重载注意事项
//1、引用作为重载条件

void func(int &a)
{
    cout << "func (int &a) 调用 " << endl;
}

void func(const int &a)
{
    cout << "func (const int &a) 调用 " << endl;
}

//2、函数重载碰到函数默认参数

void func2(int a, int b = 10)
{
    cout << "func2(int a, int b = 10) 调用" << endl;
}

void func2(int a)
{
    cout << "func2(int a) 调用" << endl;
}

int main() {
    
    int a = 10;
    func(a); //调用无const
    func(10);//调用有const

    //func2(10); //碰到默认参数产生歧义，需要避免


    return 0;
}

运行结果：

func (int &a) 调用
func (const int &a) 调用
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